Not Applicable.
Not Applicable.
The present invention relates in general to an electric traction motor drive system for an electric vehicle (EV) or a hybrid electric vehicle (HEV), and, more specifically, to the prediction of torque and power capabilities in connection with controlling the vehicle.
Worldwide demand for fuel-efficient, low-emission vehicles has led to the development of alternative powertrain architectures, such as Integrated Starter Alternator (ISA) systems for stop/start vehicles, the Electric Vehicles (EV), and the combination of an electric traction motor with a downsized internal combustion (IC) engine known as the Hybrid Electric Vehicle (HEV).
An HEV may utilize a powertrain structure combining the electric traction motor and the IC engine either in series or in parallel. Typically, the traction motors used are AC electric machines, such as induction machines, reluctance machines, brushless DC machines, or permanent magnet synchronous machines. When driving the vehicle at low speeds, the powertrain is commanded to operate in a purely electric propulsion mode. When vehicle speed increases to a certain level, the IC engine is engaged to provide power to the driveline via a mechanical clutch. After the engagement of the IC engine, the traction motor may provide torque boost to the driveline, charge the main battery, provide driveline synchronization during gear shifts, or provide active damping of driveline oscillations to improve drivability.
The traction motor is typically powered from a high voltage battery via an inverter. A DC/DC converter inside an inverter module typically converts the electric power on the high voltage bus to a lower voltage on a low voltage bus to provide electric power to other electrical loads in the vehicle and to charge a low voltage battery.
Considerable improvement in fuel economy and emission reduction can be obtained from hybrid vehicles. HEV""s permit the use of smaller sized IC engines because the electric traction motor provides power at low speeds and torque boost at high speeds. Furthermore, the reduced operating range of the IC engine allows it to be configured to operate at its highest efficiencies at all times. High efficiency is also achieved for battery charging.
In order to optimize fuel efficiency, reduce emission level, and improve driving performance, a vehicle system controller issues operating commands according to an optimal fuel efficiency map of the IC engine. The manner in which HEV and EV propulsion systems are controlled is a primary determinant of the overall efficiency obtained. Consequently, it is desirable to increase efficiency and performance by finding improved control methods and apparatus.
The present invention has the advantages of providing increased efficiency and increased performance of operation of HEV""s and EV""s by virtue of improved control based on determination of instantaneous torque and/or power capabilities of the traction motor and battery subsystem.
To optimally control various vehicle operations, both maximum and minimum torque and power capability information at transient and continuous operations of the traction motor and battery subsystem are necessary. These vehicle operations include propelling the vehicle in pure electric mode at low speeds, cranking the IC engine using the traction motor, providing torque boost from the traction motor to the driveline, charging the main battery, providing driveline synchronization during gearshifts, and providing active damping of driveline oscillations to improve drivability. A reduction in complexity of the vehicle system controller can also be achieved by incorporating xe2x80x9cavailable torquexe2x80x9d and xe2x80x9cavailable powerxe2x80x9d information into the control strategies of the vehicle system controller. In addition, by knowing torque and power capabilities of the combined traction motor and battery subsystem, the system controller can avoid issuing these commands that exceed the instantaneous capabilities of the traction motor and battery.
The present invention recognizes that at any particular operating conditions, the torque and power capabilities of the traction motor and battery subsystem can be limited by either 1) the contemporaneous torque/power capacity of the traction motor or 2) the contemporaneous power available from the high voltage battery.
In one aspect of the invention, a method is provided for estimating available torque output from a battery-powered traction motor system in a vehicle, wherein the system includes a high-voltage battery coupled to a traction motor by an inverter, wherein the inverter is controlled in response to a torque or speed command within an inverter controller, and wherein the system further includes a DC-to-DC converter coupled to the high-voltage battery to provide a reduced voltage to charge a low-voltage battery. The method comprises determining battery operating conditions of the high-voltage battery including available battery power and battery voltage. Traction motor electrical parameters such as resistance, inductances, and flux linkage corresponding to operating conditions are determined, with consideration of temperature and magnetic saturation. The battery information (such as voltage, current, and internal resistance) is transformed into synchronous coordinates. An available quadrature current corresponding to the maximum available torque is determined in response to the present machine operating conditions and the battery voltage in the synchronous coordinates. The available quadrature current is clamped in response to predetermined clamping limits. A first estimated available torque is determined in response to the clamped available quadrature current and the traction motor operating conditions. A high-voltage power usage is determined including power consumed in the DC-to-DC converter, power loss in the DC-to-DC converter, and power loss in the traction motor and inverter. An angular speed of the traction motor is measured. A second estimated available torque is determined in response to the available battery power, the high-voltage power usage, and the angular speed. A lesser one of said first and second estimated available torques is selected as the available torque output from the battery-powered traction motor system.